The invention relates to an incandescent lamp for motor vehicle headlights having two filaments and an antidazzle device.
Such an incandescent lamp is disclosed, for example, in European laid-open application EP 791 779 A2. This laid-open application describes an incandescent lamp with a secondary filament for generating the lower beam, and a primary filament for generating the upper beam in a motor vehicle headlight. Furthermore, the incandescent lamp has an antidazzle device that is arranged in the lamp vessel and shields a portion of the light generated by the secondary filament. The antidazzle device is used to produce the light/dark boundary of the lower beam. In particular, the shape of the antidazzle device is adapted appropriately for this purpose. It is disadvantageous in this case that producing the light/dark boundary requires a large portion of the light generated by the secondary filament to be shaded by the antidazzle device, with the result that it is not available for illuminating the road.
It is the object of the invention to render a larger portion of the light generated by the lower beam filament available for the illumination of the road in a generic incandescent lamp.
A substantial aspect of the present invention is that the antidazzle device is no longer used to produce the light/dark boundary, but instead the light/dark boundary is fixed solely by the position and orientation of the secondary filament with reference to the headlight reflector. The inventive incandescent lamp has the following features for this purpose:
a transparent lamp vessel with a first incandescent filament arranged therein, and a second incandescent filament arranged therein,
a lamp base in which the lamp vessel is anchored, the lamp base defining a reference plane and having a longitudinal axis that is aligned perpendicular to the reference plane, serves as reference axis, and with reference to which at least the second incandescent filament is aligned,
the first incandescent filament is aligned transverse to the reference axis, and the second incandescent filament is aligned substantially parallel to the reference axis,
the lamp base has means for installing the incandescent lamp in the correct position in a motor vehicle headlight,
an antidazzle device, arranged in the lamp vessel, for shading a portion of the light emitted by the second incandescent filament,
the second incandescent filament being arranged in such a way that, in a projection plane that is arranged perpendicular to the reference plane,
the edge, facing the antidazzle device, of the image, projected onto the projection plane, of the second incandescent filament is arranged over the entire length of the second incandescent filament between the reference axis and the antidazzle device, and
the edge, facing the antidazzle device, of the image, projected to the scale 1:1 onto the projection plane, of the second incandescent filament has a prescribed spacing from the reference axis.
When the inventive incandescent lamp is being mounted in a motor vehicle headlight, the means arranged in the lamp base for installing the lamp in the correct position between the optical axis of the headlight reflector and the reference plane of the lamp base as well as the longitudinal axis, serving as reference axis, of the lamp base produce a well defined spatial relationship such that the reference plane and the longitudinal axis of the lamp base can be used not only to adjust the incandescent filaments in the lamp, but that this adjustment at the same time also signifies an adjustment of the incandescent filaments with reference to the optical axis of the headlight reflector. When the lamp is correctly mounted in a headlight, the optical axis of the headlight reflector and the longitudinal axis of the lamp base are usually identical. According to the invention, the second incandescent filament, which is the secondary filament serving to generate the lower beam, is arranged in such a way that, in a projection plane that is arranged perpendicular to the reference plane, the edge, facing the antidazzle device, of the image, projected onto the projection plane, of the second incandescent filament is arranged over the entire length of the second incandescent filament between the reference axis and the antidazzle device, and the edge, facing the antidazzle device, of the image, projected to the scale 1:1 onto the projection plane, of the second incandescent filament has a prescribed spacing from the reference axis. This ensures that only light from a relatively narrow angular region is shaded by the surface of the second incandescent filament facing the antidazzle device, and the contour of the second incandescent filament, in particular the contour of the part of the filament surface facing the antidazzle device, can be used to produce the light/dark boundary of the lower beam. The value for the abovementioned spacing from the reference axis is preferably 0.7 mm, in order to keep as slight as possible the influence of mirror images of the secondary filaments that are generated by the lamp vessel.
The value of the abovementioned prescribed spacing is advantageously fixed with an accuracy of xc2x10.3 mm in order to permit an optimal adaptation between the lamp and headlight reflector. An even narrower tolerance limit preferably applies to the spacing from the end of the second incandescent filament, arranged closer to the reference plane, from the reference axis. At the end of the second incandescent filament arranged closer to the reference plane, the accuracy for the abovementioned prescribed spacing value of the edge, facing the antidazzle device, of the image of the second incandescent filament projected, onto the projection plane to the scale 1:1, from the reference axis is preferably fixed at approximately xc2x10.2 mm. The antidazzle device now only serves the purpose of shielding the regions of the headlight reflector from the light of the secondary filament that are reserved for the upper beam generated by the primary filament, and of shading the two incandescent filaments from one another.
In order to be able to illuminate the road with as much light as possible from the second incandescent filament, the side edges of the antidazzle device advantageously have, over the entire length of the second incandescent filament, a greater spacing from the plane, which contains the reference axis and is arranged perpendicular to the reference plane and to the projection plane, than the edge, facing the antidazzle device, of the image of the second incandescent filament projected onto the projection plane. For this purpose, the antidazzle device and the second incandescent filament are preferably arranged in such a way that, in an arbitrary plane arranged parallel to the reference plane and intersecting the second incandescent filament, the two tangents to the surface, facing the antidazzle device, of the second incandescent filament, which in each case run through a side edge of the antidazzle device, in each case form an angle of at least 10 degrees with the plane arranged perpendicular to the projection plane and to the reference plane, and containing the reference axis.
Moreover, in order to shade a sufficiently large solid angle from the light emitted by the second incandescent filament, in an arbitrary plane, arranged parallel to the reference plane and intersecting the second incandescent filament, the two tangents to the surface, averted from the antidazzle device of the second incandescent filament, which in each case run through a side edge of the antidazzle device, advantageously form an angle of at least 110 degrees with one another.
The spacing of the second incandescent filament from the reference plane is advantageously 30.0 mmxc2x10.2 mm. This relatively large spacing ensures that the lamp base is not exposed to high thermal stress during operation of the lamp. Moreover, the narrow limits for the spacing value permit an optimal adaptation of the headlight reflector to the lamp.